JP7826212B2 - Release film - Google Patents

Description

The present invention relates to a release film.

BACKGROUND ART Release films are used in the manufacturing processes of printed wiring boards, flexible circuit boards, multilayer printed wiring boards, and the like.
In the manufacturing process of a flexible circuit board, a coverlay film is heat-press bonded to a flexible circuit board body having a copper circuit formed thereon via a thermosetting adhesive or a thermosetting adhesive sheet. At this time, by placing a release film between the coverlay film and the heat-press plate, it is possible to prevent the coverlay film and the heat-press plate from adhering to each other and also to prevent problems such as adhesive seeping out and interfering with the plating process of the electrode parts.

Release films are required to have releasability that allows them to be easily peeled off after heat press bonding. To improve releasability, for example, the crystallinity of the release film is adjusted. Patent Document 1 describes a release film that has a release layer containing a polyester resin on at least one side, and the crystallinity of the release layer is 10% or more and 50% or less.

Japanese Patent Application Laid-Open No. 2016-2730

In recent years, with the trend toward thinner flexible circuit boards, further improvement in the releasability of release films has been required. In addition, in order to ensure performance such as releasability and ability to conform to irregularities (embedding ability) while also dealing with the trend toward thinner L/S (lines/spaces) of flexible circuit boards, release films made of multiple layers including a release layer and a cushion layer have also been used.
From the viewpoint of improving conformability to irregularities, it is conceivable to further soften the release film (particularly the cushion layer). However, softening the release film (particularly the cushion layer) reduces the elastic modulus and deteriorates the release properties, making it difficult to improve both the release properties and the conformability to irregularities. In addition, if the cushion layer is softened too much, there is also the problem of the resin constituting the cushion layer bleeding out during hot press bonding.

The object of the present invention is to provide a release film that has excellent releasability and ability to conform to uneven surfaces, and is less likely to cause resin bleeding.

The present invention provides a release film in which the relaxation time ( _T2 ) of the soft component at 180°C measured by the CPMG method in pulse NMR is 220 milliseconds or more and 330 milliseconds or less, and the soft component ratio at 30°C measured by the Solid Echo method in pulse NMR after exposure to the following temperature conditions is 0.1% or more and 15% or less.
[Temperature conditions]
The temperature was raised from 30° C. to 180° C. at a rate of 10° C./min, and then lowered from 180° C. to 30° C. at a rate of 10° C./min. The present invention will now be described in detail.

Heat press bonding is typically performed at a high temperature of approximately 160 to 180°C, and the release film is then peeled off after returning to room temperature. To improve both releasability and conformability to irregularities, a release film must soften at the high temperature during heat press bonding, but harden when returned to room temperature for peeling, and have an appropriate elastic modulus. To obtain a release film exhibiting such behavior, the inventors analyzed the release film using pulsed NMR, which measures ^1H nuclei. Pulse NMR allows the molecular mobility to be evaluated by dividing the obtained data into multiple components, such as hard components with high crystallinity and soft components with low crystallinity, and measuring the "relaxation time" for each component. Specifically, the relaxation time for each component is obtained by waveform-separating the obtained free induction decay curve of the spin-spin relaxation of ^1H nuclei into multiple components. The spin-spin relaxation time is also called the transverse relaxation time and is generally expressed as _T2 . The spin-lattice relaxation time is also called the longitudinal relaxation time and is generally expressed as _T1 .
The present inventors focused on the soft component with low crystallinity in the release film and investigated adjusting, within specific ranges, the relaxation time ( _T2 ) of the soft component at 180°C measured by the CPMG method using pulse NMR and the soft component ratio at 30°C measured by the Solid Echo method using pulse NMR after exposure to specific temperature conditions. The present inventors discovered that such a release film softens at high temperatures during hot press bonding, but hardens when returned to room temperature and peeled, and has an appropriate elastic modulus, thereby demonstrating excellent releasability and ability to conform to irregularities and preventing resin exudation, which led to the completion of the present invention.

The release film of the present invention has a relaxation time (T ₂ ) of the soft component at 180° C. measured by the CPMG method in pulse NMR, with a lower limit of 220 milliseconds and an upper limit of 330 milliseconds.

Here, the "soft component" refers to the low-crystalline component when the data obtained by pulsed NMR is divided into a high-crystalline component, a low-crystalline component, and a component with intermediate properties. The high-crystalline component is called the "hard component," and the component with intermediate properties is called the "middle component."
The "hard components" correspond to the parts containing intramolecular or intermolecular bonds (e.g., crystalline structures, cross-linked structures, etc.), the "soft components" correspond to the amorphous parts, and the "middle components" correspond to the parts where molecular movement is relatively possible (e.g., folded parts of crystals, etc.).
The division into components is carried out by analyzing the data (free induction decay curve) obtained by pulse NMR using the least squares method and dividing it into three parts: "hard components" with low molecular mobility, whose magnetization intensity decays quickly; "soft components" with high molecular mobility, whose magnetization intensity decays slowly; and "middle components" with properties intermediate between these two.

The "relaxation time" is the time it takes for the electron spin to return from an excited state to the ground state after a magnetic field is applied. The longer the "relaxation time," the higher the molecular mobility.
If the relaxation time ( _T2 ) of the soft component at 180°C is 220 milliseconds or more, the molecular mobility of the soft component at high temperatures during hot press bonding is high, so the release film is sufficiently softened and can exhibit excellent conformability to unevenness. If the relaxation time ( _T2 ) of the soft component at 180°C is 330 milliseconds or less, the molecular mobility of the soft component is too high, which can prevent resin from bleeding out. The preferred lower limit of the relaxation time ( _T2 ) of the soft component at 180°C is 250 milliseconds, the preferred upper limit is 310 milliseconds, the more preferred lower limit is 270 milliseconds, and the more preferred upper limit is 290 milliseconds.
The relaxation time (T ₂ ) of the soft component at 180°C can be measured by, for example, using a pulse NMR such as the minispec mq20 (manufactured by BRUKER) and analysis software (for example, TD-NMR, manufactured by BRUKER), using a release film as a measurement sample, raising the temperature from 30°C to 180°C at a heating rate of 10°C/min, maintaining it at 180°C for 10 minutes, and then measuring it by the CPMG method.

The release film of the present invention has a soft component ratio at 30° C. measured by the solid echo method using pulse NMR after exposure to the following temperature conditions, with the lower limit being 0.1% and the upper limit being 15%.
[Temperature conditions]
The temperature was increased from 30°C to 180°C at a rate of 10°C/min, and then decreased from 180°C to 30°C at a rate of 10°C/min.

The above temperature conditions are set assuming a series of steps in which heat press bonding is typically performed at a high temperature of about 160 to 180°C, followed by returning to room temperature and then peeling off the release film. If the soft component ratio at 30°C is within the above range, the crystallinity of the release film will be sufficiently high when it is returned to room temperature after being heated to the high temperature used for heat press bonding, and therefore the release film will have a moderate elastic modulus and can exhibit excellent releasability. The preferred lower limit of the soft component ratio at 30°C is 1%, the preferred upper limit is 10%, the more preferred lower limit is 3%, and the more preferred upper limit is 5%.
The soft component ratio at 30°C can be measured using, for example, a pulse NMR such as the minispec mq20 (manufactured by BRUKER) and analysis software (for example, TD-NMR, manufactured by BRUKER). More specifically, using a release film as a measurement sample, the temperature is increased from 30°C to 180°C at a temperature increase rate of 10°C/min, maintained at 180°C for 10 minutes, and then decreased from 180°C to 30°C at a temperature decrease rate of 10°C/min, and maintained at 30°C for 10 minutes, after which measurement can be performed by a solid echo method. The measurement of the soft component ratio at 30°C may be performed immediately after the measurement of the relaxation time ( _T2 ) of the soft component at 180°C.
The CPMG method and the solid echo method are both types of electromagnetic pulse irradiation conditions in pulsed NMR. Generally, the measurement method is selected depending on the length of the relaxation time. The solid echo method is used when it is desired to measure components with short relaxation times, and the CPMG method is used when it is desired to measure components with long relaxation times as well.

The method for adjusting the relaxation time ( _T2 ) of the soft component at 180°C to the above range is not particularly limited, but a method using a resin that has smaller intermolecular interactions and higher molecular mobility at 180°C as the resin constituting the release film is preferred. More specifically, as will be described later, a method using a polyolefin resin having a linear structure as the resin constituting the cushion layer can be mentioned. Furthermore, a method using, for example, a resin with a small molecular weight, a non-polar polymer, a resin without unsaturated bonds, etc. as the resin constituting the cushion layer can also be mentioned.
The method for adjusting the soft component ratio at 30°C to fall within the above range is not particularly limited, but a method that promotes crystallization when the resin is returned to room temperature after being heated to a high temperature during hot press bonding is preferred. More specifically, a method of adding a crystal nucleating agent to the cushion layer, as described below, can be mentioned. Further examples include a method of adjusting cooling conditions, a method of controlling the stereoregularity of the resin constituting the cushion layer, and a method of blending a resin with a high degree of crystallinity and a resin with a low degree of crystallinity in combination into the cushion layer.

The structure of the release film of the present invention is not particularly limited and may be a single-layer structure or a multi-layer structure, but it preferably has a release layer and a cushion layer. Furthermore, it is more preferable to have a release layer on both sides of the cushion layer.
The release layer plays a role in providing the release film with excellent releasability. Furthermore, the cushion layer improves the ability of the release film to conform to irregularities. By providing a release film with the release layer and the cushion layer, and with the release layer on both sides of the cushion layer, it becomes easy to adjust the relaxation time ( _T2 ) of the soft component at 180°C and the soft component ratio at 30°C within the above ranges, allowing the release film to exhibit even better releasability and conformability to irregularities.
The release layers on both sides may have the same resin composition or different resin compositions. The release layers on both sides may have the same thickness or different thicknesses. The release layer and the cushion layer may be in direct contact with each other and integrated, or may be integrated via an adhesive layer.

The resin constituting the release layer is not particularly limited, but is preferably at least one resin selected from the group consisting of polyester, polyolefin, and polystyrene, as this improves the releasability of the release film.
The polyester preferably contains an aromatic polyester resin. The polyolefin preferably contains poly(4-methyl-1-pentene) or an alicyclic olefin resin. The polystyrene preferably contains a polystyrene resin having a syndiotactic structure. In particular, the release layer more preferably contains an aromatic polyester resin, as this provides excellent conformability to irregularities and excellent resistance to bleeding of the adhesive formed on the coverlay film.
When the resins exemplified here are used, the release layer becomes relatively hard, and therefore the release layer alone (single layer) is thought to contain almost no soft component at 30°C.

The aromatic polyester resin is not particularly limited, but a crystalline aromatic polyester resin is preferred.Specific examples include polyethylene terephthalate resin, polybutylene terephthalate resin, polyhexamethylene terephthalate resin, polyethylene naphthalate resin, polybutylene naphthalate resin, and butanediol terephthalate polytetramethylene glycol copolymer.These aromatic polyester resins may be used alone or in combination of two or more.Among them, polybutylene terephthalate resin is preferred from the viewpoint of a balance of heat resistance, releasability, conformability to uneven surfaces, etc.
Also preferred is a mixed resin obtained by mixing a polybutylene terephthalate resin with a block copolymer of polybutylene terephthalate and an aliphatic polyether. The aliphatic polyether is not particularly limited, and examples thereof include polyethylene glycol, polydiethylene glycol, polypropylene glycol, and polytetramethylene glycol.

From the viewpoint of film formability, the aromatic polyester resin preferably has a melt volume flow rate of 30 cm ³ /10 min or less, more preferably 20 cm ³ /10 min or less. The melt volume flow rate can be measured in accordance with ISO 1133 at a temperature of 250°C and a load of 2.16 kg.

Commercially available examples of the above aromatic polyester resins include "Pelprene (registered trademark)" (manufactured by Toyobo Co., Ltd.), "Hytrel (registered trademark)" (manufactured by DuPont-Toray Co., Ltd.), "Duranex (registered trademark)" (manufactured by Polyplastics Co., Ltd.), and "NovaDuran (registered trademark)" (manufactured by Mitsubishi Engineering-Plastics Corporation).

The polyolefin containing poly(4-methyl-1-pentene) preferably contains 90% by weight or more of poly(4-methyl-1-pentene) resin.
As the poly(4-methyl-1-pentene) resin, for example, a commercially available product such as TPX (registered trademark) manufactured by Mitsui Chemicals, Inc. can be used.

The alicyclic olefin resin is an olefin resin having a cyclic aliphatic hydrocarbon in the main chain or side chain, and from the viewpoints of heat resistance, strength, etc., thermoplastic saturated norbornene resin is preferred.
Examples of the thermoplastic saturated norbornene resin include resins obtained by hydrogenating a ring-opening polymer or ring-opening copolymer of a norbornene monomer (after, if necessary, modification such as maleic acid addition or cyclopentadiene addition). Other examples include resins obtained by addition polymerization of a norbornene monomer, resins obtained by addition polymerization of a norbornene monomer and an olefinic monomer such as ethylene or an α-olefin, and resins obtained by addition polymerization of a norbornene monomer and a cyclic olefinic monomer such as cyclopentene, cyclooctene, or 5,6-dihydrodicyclopentadiene. Modified versions of these resins are also included.

The polystyrene containing the polystyrene resin having a syndiotactic structure preferably contains 70% by weight or more and 90% by weight or less of the polystyrene resin having a syndiotactic structure.
The polystyrene resin having a syndiotactic structure is a resin having a stereoregular structure in which phenyl groups and substituted phenyl groups, which are side chains, are alternately positioned in opposite directions relative to the main chain formed from carbon-carbon sigma bonds.

The polystyrene resin having the syndiotactic structure is not particularly limited. Examples include polystyrene, poly(alkylstyrene), poly(arylstyrene), poly(halogenated styrene), poly(halogenated alkylstyrene), poly(alkoxystyrene), and poly(vinyl benzoate ester), each having a syndiotacticity of 75% or more in racemic diads or 30% or more in racemic pentads. Other examples include hydrogenated polymers of these, mixtures of these, and copolymers containing these as the main component. Examples of the polystyrene resin having the syndiotactic structure include commercially available products such as XAREC (registered trademark) manufactured by Idemitsu Kosan Co., Ltd.

The release layer may contain a rubber component, which improves the ability of the release layer to conform to the irregularities of the release film.
The rubber component is not particularly limited, and examples thereof include natural rubber, styrene-butadiene copolymer, polybutadiene, polyisoprene, acrylonitrile-butadiene copolymer, ethylene-propylene copolymer (EPM, EPDM), polychloroprene, butyl rubber, acrylic rubber, silicone rubber, urethane rubber, etc. Further, examples of the rubber component include olefin-based thermoplastic elastomer, styrene-based thermoplastic elastomer, vinyl chloride-based thermoplastic elastomer, ester-based thermoplastic elastomer, amide-based thermoplastic elastomer, etc.

The release layer may contain a stabilizer.
The stabilizer is not particularly limited, and examples thereof include hindered phenol-based antioxidants and heat stabilizers.
The hindered phenol-based antioxidant is not particularly limited, and examples thereof include 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene and 3,9-bis{2-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)-propionyloxy]-1,1-dimethylethyl}-2,4,8,10-tetraoxaspiro[5,5]undecane. The heat stabilizer is not particularly limited, and examples thereof include tris(2,4-di-t-butylphenyl)phosphite, trilauryl phosphite, 2-t-butyl-α-(3-t-butyl-4-hydroxyphenyl)-p-cumenylbis(p-nonylphenyl)phosphite, dimyristyl 3,3′-thiodipropionate, distearyl 3,3′-thiodipropionate, pentaerythryl tetrakis(3-laurylthiopropionate), and ditridecyl 3,3′-thiodipropionate.

The release layer may further contain conventional additives such as fibers, inorganic fillers, flame retardants, ultraviolet absorbers, antistatic agents, inorganic substances, and salts of higher fatty acids.

The thickness of the release layer is not particularly limited, but by making the thickness of the release layer relatively thin and the thickness of the cushion layer relatively thick, the contribution of the cushion layer to the entire release film can be increased, and the soft component ratio can be increased. This allows the release film to exhibit better conformability to uneven surfaces. The preferred lower limit of the thickness of the release layer is 10 μm, and the preferred upper limit is 40 μm. If the thickness of the release layer is 10 μm or more, the heat resistance of the release film is improved. If the thickness of the release layer is 40 μm or less, the conformability of the release film to uneven surfaces is improved. The more preferred lower limit of the thickness of the release layer is 15 μm, and the more preferred upper limit is 30 μm.

The resin constituting the cushion layer is not particularly limited, but polyolefin resin is preferred.
The polyolefin resin is not particularly limited, and examples thereof include polyethylene resins (e.g., high-density polyethylene, low-density polyethylene, linear low-density polyethylene), polypropylene resins, ethylene-vinyl acetate copolymers, etc. Further examples include ethylene-acrylic monomer copolymers such as ethylene-methyl methacrylate copolymers, ethylene-ethyl acrylate copolymers, and ethylene-acrylic acid copolymers. These polyolefin resins may be used alone or in combination of two or more. Among these, polyethylene resins are preferred because they can provide a release film that exhibits superior releasability and ability to conform to uneven surfaces.

The polyolefin resin preferably contains a polyolefin resin having a linear structure.
Specifically, for example, when the polyolefin resin contains the polyethylene resin, it is preferable to use an appropriate amount of linear high-density polyethylene (HDPE) in addition to the highly branched low-density polyethylene (LDPE) that has traditionally been used in cushion layers. This makes it easy to adjust the relaxation time ( _T2 ) of the soft component at 180°C within the above range, allowing the release film to exhibit better conformability to uneven surfaces. This is because, compared to highly branched low-density polyethylene (LDPE), linear high-density polyethylene (HDPE) has weaker intermolecular interactions and higher molecular mobility at temperatures above its melting point.
Furthermore, high density polyethylene (HDPE) with a linear structure easily assumes a crystalline structure when cooled to a temperature below its melting point and then returned to room temperature, thereby increasing the degree of crystallinity. Therefore, by using high density polyethylene (HDPE), it becomes easy to adjust the soft component ratio at 30°C to fall within the above range, and the release film can also exhibit better releasability.

The content of the polyolefin resin having a linear structure in the cushion layer is not particularly limited, but from the viewpoint of adjusting the relaxation time ( _T2 ) of the soft component at 180°C and the soft component ratio at 30°C within the above ranges, a preferred lower limit is 5% by weight and a preferred upper limit is 25% by weight. When the content of the polyolefin resin having a linear structure is 5% by weight or more, the release film is more likely to exhibit excellent releasability and conformability to unevenness. When the content of the polyolefin resin having a linear structure is 25% by weight or less, the molecular mobility of the soft component is too high, which can further prevent the resin from bleeding out. A more preferred lower limit of the content of the polyolefin resin having a linear structure is 10% by weight, a more preferred upper limit is 20% by weight, and an even more preferred lower limit is 15% by weight.

The content of the polyolefin resin in the cushion layer is not particularly limited, but a preferred lower limit is 50% by weight and a preferred upper limit is 90% by weight. If the content of the polyolefin resin is 50% by weight or more, the cushion layer will have sufficient flexibility and will have improved ability to conform to the irregularities of the release film. If the content of the polyolefin resin is 90% by weight or less, the adhesion between the release layer and the cushion layer will be improved. A more preferred lower limit of the polyolefin resin content is 60% by weight, and an even more preferred lower limit is 65% by weight. A more preferred upper limit of the polyolefin resin content is 80% by weight, and an even more preferred upper limit is 75% by weight.

The cushion layer may contain the resin that constitutes the release layer. When the cushion layer contains the resin that constitutes the release layer, the adhesion between the release layer and the cushion layer is improved. It is more preferable that the cushion layer contains the main component resin of the release layer. Here, the main component resin of the release layer means the resin that is contained in the largest amount among the resins contained in the release layer.

The content of the resin constituting the release layer in the cushion layer is not particularly limited, but a preferred lower limit is 10% by weight and a preferred upper limit is 50% by weight. If the content of the resin constituting the release layer is 10% by weight or more, the adhesion between the release layer and the cushion layer is improved. If the content of the resin constituting the release layer is 50% by weight or less, the cushion layer will have sufficient flexibility and will have improved ability to conform to the unevenness of the release film. A more preferred lower limit for the content of the resin constituting the release layer is 20% by weight, and an even more preferred lower limit is 25% by weight. A more preferred upper limit for the content of the resin constituting the release layer is 40% by weight, and an even more preferred upper limit is 35% by weight.

The cushioning layer may further contain resins such as polystyrene, polyvinyl chloride, polyamide, polycarbonate, polysulfone, polyester, etc.

The cushion layer preferably further contains a crystal nucleating agent.
The inclusion of the crystal nucleating agent in the cushion layer promotes crystallization of the resin constituting the cushion layer when the temperature is returned to room temperature after being heated to a high temperature during hot press bonding, which makes it easy to adjust the soft component ratio at 30°C within the above range, and allows the release film to exhibit better releasability.

The crystal nucleating agent is not particularly limited as long as it is a compound that promotes the crystallization of a polymer compound. Examples of crystal nucleating agents for polypropylene resin include metal phosphates, metal carboxylates, metal pimelic acids, metal rosins, sorbitol nucleating agents, quinacridone, cyanine blue, and talc.
Examples of the metal carboxylate nucleating agent include sodium benzoate, aluminum dibenzoate, potassium benzoate, etc. Examples of the sorbitol nucleating agent include dibenzylidene sorbitol, di-alkyl-benzylidene sorbitol, etc.
Examples of crystal nucleating agents for the polyethylene resin include cyclohexane-1,2-dicarboxylate, anthracene, potassium hydrogen phthalate, benzoic acid compounds, ultra-high molecular weight polyethylene, metal phosphate salts, talc, calcium carbonate, titanium dioxide, silicon dioxide, barium sulfate, vermiculite, and carbon nanotubes.

The content of the nucleating agent in the cushion layer is not particularly limited, but a preferred lower limit is 0.5% by weight, a preferred upper limit is 5% by weight, a more preferred lower limit is 1% by weight, and a more preferred upper limit is 3% by weight. If the content of the nucleating agent is 1% by weight or more, the release film can exhibit better release properties. If the content of the nucleating agent is 3% by weight or less, the flexibility of the cushion layer can be maintained while suppressing resin exudation. An even more preferred lower limit of the content of the nucleating agent is 1.5% by weight, and an even more preferred upper limit is 2% by weight.

The cushion layer may further contain additives such as fibers, inorganic fillers, flame retardants, ultraviolet absorbers, antistatic agents, inorganic substances, higher fatty acid salts, etc. In particular, when the cushion layer contains the inorganic fillers, the exudation of resin can be further suppressed without adversely affecting the relaxation time ( _T2 ) of the soft component at 180°C and the soft component ratio at 30°C.

The cushion layer may have a single-layer structure consisting of a single layer, or a multi-layer structure consisting of a laminate of multiple layers. If the cushion layer has a multi-layer structure, the multiple layers may be laminated together via an adhesive layer.

Although the thickness of the cushion layer is not particularly limited, by making the thickness of the release layer relatively thin and the thickness of the cushion layer relatively thick, the contribution of the cushion layer to the entire release film can be increased and the soft component ratio can be increased, thereby allowing the release film to exhibit better conformability to unevenness.
The cushion layer preferably has a lower limit of 15 μm and an upper limit of 200 μm. If the cushion layer has a thickness of 15 μm or more, the ability to conform to the irregularities of the release film is improved. If the cushion layer has a thickness of 200 μm or less, exudation of resin from the cushion layer at the film edge during heat press bonding can be suppressed. The cushion layer more preferably has a lower limit of 30 μm and an upper limit of 150 μm.

The method for producing the release film of the present invention is not particularly limited, and examples thereof include a water-cooled or air-cooled coextrusion inflation method, a coextrusion T-die film-forming method, a solvent casting method, and a hot press molding method.
In the case of a structure having the release layers on both sides of the cushion layer, a method of preparing a film to be one of the release layers, laminating the cushion layer on this film by extrusion lamination, and then dry laminating the other release layer can be used. Alternatively, a method of dry laminating the film to be one of the release layers, the film to be the cushion layer, and the film to be the other release layer can be used.
Among these, the co-extrusion T-die method is preferred because it allows excellent control of the thickness of each layer.

The use of the release film of the present invention is not particularly limited, but it can be suitably used in the manufacturing processes of printed wiring boards, flexible circuit boards, multilayer printed wiring boards, etc. Specifically, for example, in the manufacturing process of flexible circuit boards, the release film of the present invention can be used when hot-press bonding a coverlay film to a flexible circuit board main body having a copper circuit formed thereon via a thermosetting adhesive or a thermosetting adhesive sheet.

According to the present invention, a release film can be provided that has excellent releasability and ability to conform to uneven surfaces, and is less likely to cause resin bleeding.

The following examples further illustrate aspects of the present invention, but the present invention is not limited to these examples.

Example 1
(1) Production of release film 60 parts by weight of polybutylene terephthalate resin (PBT) and 40 parts by weight of a copolymer of polybutylene terephthalate and polytetramethylene glycol (PBT/PTMG copolymer) were mixed to obtain a resin composition for a release layer.
A resin composition for a cushion layer was obtained by mixing 39 parts by weight of low-density polyethylene (LDPE) (Suntec-LD (M2102), manufactured by Asahi Kasei Corporation), 59.5 parts by weight of ethylene-methyl methacrylate copolymer (EMMA1) (Acryft WH401, manufactured by Sumitomo Chemical Co., Ltd.), and 1.5 parts by weight of a PE crystal nucleating agent (Rikemaster CN, manufactured by Riken Vitamin Co., Ltd.).
The obtained resin composition for the release layer and the resin composition for the cushion layer were co-extruded into a three-layer structure using an extruder with a T-die width of 400 mm, to obtain a release film having a cushion layer (thickness 90 μm) and a release layer (thickness 15 μm on each side) on both sides. The extruder used was a GM30-28 extruder manufactured by GM Engineering, with a screw diameter of 30 mm and an L/D of 28.

(2) Pulse NMR Measurement As a measurement sample, about 10 g of the release film was rolled into a cylindrical shape and introduced into a glass sample tube with a diameter of 10 mm (manufactured by BRUKER, product number 1824511, length 180 mm, flat bottom) so as to have a height of 20 mm.

Using a pulse NMR "the minispec mq20" (manufactured by BRUKER), the release film in the sample tube was heated from 30°C to 180°C at a heating rate of 10°C/min, and after maintaining at 180°C for 10 minutes, the relaxation time ( _T2 ) of the soft component at 180°C was determined by the CPMG method.
[CPMG method measurement conditions]
Scans: 128 times
Recycle Delay: 2sec
90-180 plus searation: 0.05
Total number of acquired echoes: 3000

Furthermore, using a pulse NMR "the minispec mq20" (manufactured by BRUKER), the soft component ratio at 30°C was determined. More specifically, the release film in the sample tube was heated from 30°C to 180°C at a heating rate of 10°C/min, maintained at 180°C for 10 minutes, and then cooled from 180°C to 30°C at a cooling rate of 10°C/min, maintained at 30°C for 10 minutes, and then the soft component ratio at 30°C was determined by a solid echo method.
[Solid Echo method measurement conditions]
Scans:64times
Recycle Delay: 2sec
Acquisition scale: 1ms

The relaxation time (T ₂ ) of the soft component at 180° C. by the CPMG method and the soft component ratio at 30° C. by the Solid Echo method were calculated by the following methods.
The free induction decay curve of spin-spin relaxation of ^1H nuclei obtained as a result of pulsed NMR measurement (vertical axis: magnetization intensity, horizontal axis: time) was waveform separated into three curves derived from the three components of soft, middle, and hard components, and the component ratios and relaxation times of the soft, middle, and hard components were determined. Waveform separation was performed by fitting using both Gaussian and exponential types. Specifically, using the analysis software "TD-NMRA (Version 4.3 Rev 0.8)" manufactured by BRUKER, fitting was performed using Gaussian type for the hard component and exponential type for the middle and soft components according to the product manual in the Solid Echo method at 30°C. In the CPMG method at 180°C, fitting was performed using exponential type for all of the hard, middle, and soft components. In the solid echo method, fitting was performed using points up to 0.5 milliseconds on the obtained free induction decay curve (relaxation curve), while in the CPMG method, fitting was performed using all points. The following equation was used for fitting, and the method of least squares was used.

Here, Y is the free induction decay curve, and w1, w2, and w3 are Weibull coefficients. In the Solid Echo method, w1 takes a value of 2, and w2 and w3 take a value of 1, while w1 to w3 take a value of 1 in the CPMG method. A1 is the component ratio (unit: %) of the hard component, B1 is the middle component, and C1 is the soft component, and A1 + B1 + C1 = 100 is satisfied. T2A is the relaxation time (unit: milliseconds) of the hard component, T2B is the middle component, and T2C is the relaxation time (unit: milliseconds) of the soft component, and T2A < T2B < T2C is satisfied. t is time (unit: milliseconds).

In the examples of the present invention, the Recycle Delay value is set to 2 seconds, but if an appropriate measurement result (relaxation curve) cannot be obtained, a value five times the _T1 (spin-lattice relaxation time; longitudinal relaxation time) is set. Generally, the saturation recovery method or the inversion recovery method is applied to _T1 measurement.

(Examples 2 to 5, Comparative Examples 1 to 6)
A release film was obtained in the same manner as in Example 1, except that the composition of the cushion layer was changed as shown in Table 1. The materials shown in Table 1 were as follows.

High-density polyethylene (HDPE) (Suntec-HD (F371), manufactured by Asahi Kasei Corporation)
EMMA2 (Acryft WD106, manufactured by Sumitomo Chemical Co., Ltd.)

<Evaluation>
The release films obtained in the examples and comparative examples were evaluated as follows. The results are shown in Table 1.

(1) Evaluation of releasability The release film was placed on an epoxy adhesive sheet (CISV2535, manufactured by Nikkan Industries Co., Ltd.) and hot-pressed for 5 minutes at 180°C and 30 kgf/ ^cm² . It was then cut to a width of 25 mm and subjected to a peel test at a test speed of 500 mm/min and a peel angle of 180°. A peel strength of 20 gf/ ^cm² or less was evaluated as ○, a peel strength of more than 20 gf/ ^cm² to 30 gf/ ^cm² or less was evaluated as ×, and a peel strength of more than 30 gf/ ^cm² was evaluated as XX.

(2) Evaluation of Conformability to Uneven Surfaces A coverlay film (12.5 cm x 12.5 cm, polyimide thickness 25 μm, epoxy adhesive layer thickness 35 μm) with a φ = 1 mm hole was laminated onto the copper foil surface of a copper-clad laminate (CCL) (12.5 cm x 12.5 cm, polyimide thickness 25 μm, copper foil thickness 35 μm) so that the epoxy adhesive layer was in contact with the coverlay film. A release film was then laminated onto the coverlay film. This laminate was heat-pressed for ² minutes at 180 °C and 30 kgf/cm². The release film was then peeled off, and the epoxy adhesive that had flowed onto the copper-clad laminate (CCL) was observed under an optical microscope. The exudation width of the epoxy adhesive was measured at 12 points and the average value was calculated to evaluate the conformability of the release film to uneven surfaces. When the average width of the exuded epoxy adhesive was less than 55 μm, it was evaluated as ◯, when it was 55 μm or more and 65 μm or less, it was evaluated as Δ, and when it exceeded 65 μm, it was evaluated as ×.

(3) Evaluation of resin seepage The release film was cut into 10 cm squares. A 25 cm square SUS plate, cushion paper, SiPET sheet, release film, SiPET sheet, cushion paper, and a 25 cm square SUS plate were laminated in this order and heat-pressed using a slide-type vacuum heater press (MKP-3000v-MH-ST, manufactured by Mikado Technos Co., Ltd.). The distance between the end of the resin constituting the cushion layer that had seeped out of the release film and the end of the release layer of the release film was measured and used as the seepage distance. A seepage distance of 1 mm or less was evaluated as ◯, a seepage distance of more than 1 mm but not more than 2 mm was evaluated as △, and a seepage distance of more than 2 mm was evaluated as ×.

According to the present invention, a release film can be provided that has excellent releasability and ability to conform to uneven surfaces, and is less likely to cause resin bleeding.

Claims (5)

The relaxation time (T ₂ ) of the soft component at 180° C., as measured by the CPMG method in pulsed NMR, is 220 milliseconds or more and 330 milliseconds or less, and
After exposure to the following temperature conditions, the soft component ratio at 30°C measured by pulse NMR using the Solid Echo method is 0.1% or more and 15% or less,
a release layer and a cushion layer, the release layer being disposed on both sides of the cushion layer;
The cushion layer contains a polyolefin resin.
A release film characterized by:
[Temperature conditions]
The temperature was increased from 30°C to 180°C at a rate of 10°C/min, and then decreased from 180°C to 30°C at a rate of 10°C/min. 2. The release film according to claim 1 , wherein the polyolefin resin contains a polyethylene resin. 3. The release film according to claim 1 , wherein the polyolefin resin contains a polyolefin resin having a linear structure. 4. The release film according to claim 1 , wherein the cushion layer contains a crystal nucleating agent. 5. The release film according to claim 1 , wherein the release layer contains at least one resin selected from the group consisting of polyester, polyolefin, and polystyrene.